This is I suppose the central recurring joke of Don Quijote, and part of its claim to greatness. All that our hero thinks, sees, or imagines appears in the light of what he has read. He doesn't see the world straight on, and his taking a common inn for a castle introduces the first of an endless series of comic set pieces.

But do we see the world straight on, either? How has what we have read made us take inns for castles?

If I read the book of Genesis, and, in looking at my fellow human beings thereafter, see them as created in the image and likeness of God, am I seeing castles rather than inns?

And if I see the world in the light of reading Don Quijote de la Mancha, how do I think, see, or imagine the world differently?